Bioceramic coating of hydroxyapatite on titanium substrate with Nd-YAG laser

The ability to bond to bone tissue is a unique property of bioactive ceramics. Hydroxyapatite (HAp) is one of the potential bioceramics candidates due to its superior bio-compatibility. Significant effort has been devoted to coat HAp ceramics on metallic substrates. Most of these processes, such as ion-beam sputter coating, thermal spraying, and flame spraying, are high temperature line of sight processes, which suffer from undesirable phase formation and weak metal/HAP bonding strength. This paper presents a unique process to coat HAp powders on titanium substrates at low temperature and enhance the coating/substrate interface by laser surface engineering. Nd-YAG laser transmits HAp powders and the laser power is absorbed by titanium substrate to produce a thin layer of molten region. During coating process, HAp powders are kept at low temperature before they are entrapped in metallic layer. Scanning electron microscope (SEM) was used to investigate the microstructure of coating; the chemical composition of the coating is determined by energy dispersive spectrometry (EDS). Mechanical properties of the interface between coating and Ti substrate were investigated by nanoindentation.     

Plasma-sprayed zirconia bond coat as an intermediate layer for hydroxyapatite coating on titanium alloy substrate

This study aims to strengthen the bonding at HA coating/Ti–6Al–4V interface by adding an intermediate ZrO₂ bond coat between them. The bonding strength of the HA/ZrO₂ coating was evaluated with the separately prepared HA coating as control. The phase, microstructure and chemistry, and surface roughness of the plasma-sprayed two-layer HA/ZrO₂ coating on Ti–6A1–4V substrate were investigated by X-ray diffractometry, scanning electron microscopy, and surfcorder, respectively. Experimental results indicate that the bonding strength increases from 28.6±3.22 MPa for HA coating to 36.2±3.02 MPa for HA/ZrO₂ composite coating. Elemental analysis employed on the surface of ZrO₂ bond coat, on which the HA top coat was first dissolved completely in HCl acid, reveals the sign of diffusion of calcium ions from HA to ZrO₂ bond coat. In addition, rougher surface morphology provided by ZrO₂ bond coat is also considered to aid in the bonding at HA/ZrO₂ interface. Similar coating system done by other researchers is compared and discussed.     

Synthesized silicon-substituted hydroxyapatite coating on titanium substrate by electrochemical deposition

Silicon-substituted hydroxyapaptite (Si-HA) coatings were prepared on titanium substrates by electrolytic deposition technique in electrolytes containing Ca²⁺, PO₄ ³⁻ and SiO₃ ²⁻ ions with various SiO₃ ²⁻/(PO₄ ³⁻ + SiO₃ ²⁻) molar ratios(η_si). The deposition was all conducted at a constant voltage of 3.0 V, with titanium substrate as cathode and platinum as anode, for 1 h at 85°C. The coatings thus prepared were characterized with inductively coupled plasma (ICP), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field-emission-type scanning electron microscope (FSEM). The results show that the silicon amount in the coatings increases linearly to about 0.48 wt% at first with increasing η_si between 0 and 0.03, then increases slowly to about 0.55 wt% between 0.03 and 0.10 and finally maintains almost at a level around 0.55 wt% between 0.10 and 0.30. The tree-like Si-HA crystals are observed in the coatings prepared in the electrolyte of η_si = 0.20. And the presence of silicon in electrolytes decreases the thickness of the coatings, with effect being more significant as η_si increased. Additionally, the substitution of Si causes some OH⁻ loss and changes the lattice parameters of hydroxyapatite (HA).     

Characterization of the chemically deposited hydroxyapatite coating on a titanium substrate

Bioactive hydroxyapatite (HA) coating on titanium (Ti) implant can be used as a drug delivery device. A controlled release of drug around the implant requires the incorporation of drug into the coating material during the coating process. HA coating was prepared using a two-step procedure in conditions suitable for simultaneous incorporation of the protein-based drug into the coating material. Monetite coating was deposited on Ti substrate in acidic condition followed by the transformation of the monetite coating to HA. X-ray diffraction (XRD) confirmed the formation of the monetite phase at the first step of the coating preparation, which was transformed into HA at the second step. Fourier transform infrared spectroscopy demonstrated typical bands of a crystallized carbonated HA with A- and B-type substitution, which was confirmed by the XRD refinement of the structural parameters. Scanning electron microscope was used to observe the morphology of monetite and HA coatings. Adhesion of the coatings was measured using a scratch tester. The critical shearing stress was found to be 84.20 ± 1.27 MPa for the monetite coating, and 44.40 ± 2.39 MPa for the HA coating.     

Porous low modulus Ti40Nb compacts with electrodeposited hydroxyapatite coating for biomedical applications

Porous ß-type non-toxic Ti40Nb alloy was prepared by compaction of mechanically alloyed powder mixed with NaCl or Mg particles as space-holder material. The compacts with porosity of 36–80% demonstrated a very low Young's modulus of ~ 1.5–3 GPa and compression strength of ~ 10–35 MPa, which is suitable for potential implant material application. Porous samples were electrochemically covered with hydroxyapatite. The influence of the deposition time and of the electrolyte concentrations on the morphology of the hydroxyapatite coating was studied. It is demonstrated that a homogenous coating of hydroxyapatite crystals with different shape and size can be obtained on the surface of the porous samples.     

Microstructural characterization of hydroxyapatite coating on titanium

The microstructure of hydroxyapatite plasma sprayed onto titanium alloy has been studied by using transmission electron microscopy. It has been shown that while substantial portions of the coating are crystalline hydroxyapatite, regions of amorphous calcium phosphate with Ca/P ratios of 0.6–1.0 are also present, both in the coatings and at the metal-ceramic interface. The microstructures observed have also been found to be consistent with devitrification of the amorphous calcium phosphates producing regions of very fine grained hydroxyapatite. A calcium titanate phase has also been detected at the metal-ceramic interface produced by the chemical reaction of hydroxyapatite to titanium.     

Preparation of hydroxyapatite-containing titania coating on titanium substrate by micro-arc oxidation

Hydroxyapatite-containing titania coatings on titanium substrates were formed by micro-arc oxidation (MAO) in electrolyte containing calcium acetate monohydrate (CH₃COO)₂Ca·H₂O) and sodium phosphate monobasic dihydrate (NaH₂PO₄·2H₂O) using a pulse power supply. Scanning electron microscopy (SEM) with Energy dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD) were employed to characterize the microstructure, elemental composition and phase components of the coatings. The coatings were rough and porous, without apparent interface to the titanium substrates. All the oxidized coatings contained Ca and P as well as Ti and O, and the porous coatings were made up of anatase, rutile and hydroxyapatite. Such MAO films are expected to have significant applications as artificial bone joints and dental implants.     

Sol-gel derived hydroxyapatite coatings on titanium substrate

Biomaterials, in particular those used for orthopaedic prostheses, consist of a metallic substrate, exhibiting excellent mechanical properties, coated with a ceramic layer, which guarantees resistance to the corrosion and an elevated bioactivity. In this paper the preparation of sol-gel films of hydroxyapatite, HA (Ca₁₀(PO₄)₆(OH)₂), on titanium substrate is described. The samples were obtained through the dip-coating method, starting from a colloidal suspension of hydroxyapatite. In order to increase the adhesion between the HA film and the metallic substrate, the same substrate has been preliminarily coated either with titanium oxide, TiO₂ (in the anatase or rutile phase), or calcium titanate, CaTiO₃ (perovskite). Also these latter films have been deposited from a sol-gel solution. The characterization of the films through XRD, SEM, and AFM gave good results for the crystallinity of the deposited HA; for what concerns the sample morphology, the films turned out to be homogeneous and crack-free.     

钛涂覆多孔羟基磷灰石涂层的制备及其生物活性

在纯钛基体表面通过电泳沉积的方法制得壳聚糖/羟基磷灰石(CS/HA)复合涂层, 然后将复合涂层烧结形成多孔HA涂层。采用SEM对多孔HA涂层的形貌进行观察, XRD分析涂层的物相组成, 粘结拉伸实验测定涂层与基体的结合强度, 1.5倍人体模拟体液(1.5SBF)浸泡测定涂层的生物活性。结果表明: 当悬浮液中CS与HA质量比为1∶1时, 制得的CS/HA复合涂层经过700℃烧结处理, 涂层中CS热分解致孔形成多孔HA涂层, 孔径在10~25 μm, 涂层与基体的结合强度可达19.5 MPa; 在1.5SBF中浸泡5天后, 多孔HA涂层表面完全碳磷灰石化, 呈现较好的生物活性。      

Surface microstructure and cell biocompatibility of silicon-substituted hydroxyapatite coating on titanium substrate prepared by a biomimetic process

Silicon-substituted hydroxyapatite (Si-HA) coatings with 0.14 to 1.14 at.% Si on pure titanium were prepared by a biomimetic process. The microstructure characterization and the cell compatibility of the Si-HA coatings were studied in comparison with that of hydroxyapatite (HA) coating prepared in the same way. The prepared Si-HA coatings and HA coating were only partially crystallized or in nano-scaled crystals. The introduction of Si element in HA significantly reduced P and Ca content, but densified the coating. The atom ratio of Ca to (P + Si) in the Si-HA coatings was in a range of 1.61–1.73, increasing slightly with an increase in the Si content. FTIR results displayed that Si entered HA in a form of SiO₄ unit by substituting for PO₄ unit. The cell attachment test showed that the HA and Si-HA coatings exhibited better cell response than the uncoated titanium, but no difference was observed in the cell response between the HA coating and the Si-HA coatings. Both the HA coating and the Si-HA coatings demonstrated a significantly higher cell growth rate than the uncoated pure titanium (p < 0.05) in all incubation periods while the Si-HA coating exhibited a significantly higher cell growth rate than the HA coating (p < 0.05). Si-HA with 0.42 at.% Si presented the best cell biocompatibility in all of the incubation periods. It was suggested that the synthesis mode of HA and Si-HA coatings in a simulated body environment in the biomimetic process contribute significantly to good cell biocompatibility.     

Antibacterial efficacy,corrosion resistance,and cytotoxicity studies of copper-substituted carbonated hydroxyapatite coating on titanium substrate

This work elucidated the antibacterial efficacy, corrosion resistance, and cytotoxicity of electroplated copper-substituted hydroxyapatite (CuHAP) coating on titanium (Ti). The fabricated CuHAP coatings were characterized by scanning electron microscopy, energy-dispersive X-ray analysis spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction studies. The CuHAP coating had needle-like apatite crystals, the doping of Cu²⁺ into HAP reduced porosity, and the coating became denser. The CuHAP crystals were carbonated with a few of Cu²⁺ incorporation (about 0.80 wt%). The Cu²⁺ ions were homogenously deposited into HAP films. Potentiodynamic polarisation test revealed that the CuHAP coating provided good barrier characteristics and achieved superior corrosion protection for Ti substrates. The in vitro antibacterial activity of as-prepared CuHAP coating was evaluated against Escherichia coli and was found to be effectively high against bacterial colonization. Bioactivity test conducted by soaking the coatings in simulated body fluid demonstrated that CuHAP coating can quickly induce bone-like apatite nucleation and growth. In vitro biocompatibility tests, MTT, were employed to assess the cytotoxicity of CuHAP coating with osteoblast-like MC3T3-E1 cells. The obtained HAP coating doped with a low content of Cu²⁺ exhibited good cytocompatibility and had no toxicity toward MC3T3-E1.     

Electrolytic deposition of magnesium-substituted hydroxyapatite crystals on titanium substrate

Electrolytic deposition of magnesium-substituted hydroxyapatite (Mg-HAp) coatings on titanium was investigated and Mg-HAp crystals with up to 2 wt.% Mg²⁺ were deposited in electrolytes with various Mg²⁺ concentration. The incorporation of Mg substantially changed the morphology of the HAp crystals and decreased the crystal size and crystallinity of the HAp. The similarity with natural dentin and bone in composition and the increased specific surface of the Mg-HAp coatings on the Ti substrates were believed to benefit the bioactivity and the drug-carrying properties of the coatings.     

Electrophoretic-deposited novel ternary silk fibroin/graphene oxide/hydroxyapatite nanocomposite coatings on titanium substrate for orthopedic applications

The combination of graphene oxide (GO) with robust mechanical property, silk fibroin (SF) with fascinating biological effects and hydroxyapatite (HA) with superior osteogenic activity is a competitive approach to make novel coatings for orthopedic applications. Herein, the feasibility of depositing ternary SF/GO/HA nanocomposite coatings on Ti substrate was firstly verified by exploiting electrophoretic nanotechnology, with SF being used as both a charging additive and a dispersion agent. The surface morphology, microstructure and composition, in vitro hemocompatibility and in vitro cytocompatibility of the resulting coatings were investigated by SEM, Raman, FTIR spectra and biocompatibility tests. Results demonstrated that GO, HA and SF could be co-deposited with a uniform, smooth thin-film morphology. The hemolysis rate analysis and the platelet adhesion test indicated good blood compatibility of the coatings. The human osteosarcoma MG63 cells displayed well adhesion and proliferation behaviors on the prepared coatings, with enhanced ALP activities. The present study suggested that SF/GO/HA nanocomposite coatings could be a promising candidate for the surface functionalization of biomaterials, especially as orthopedic implant coating.     

Colloidal characterization and electrophoretic deposition of hydroxyapatite on titanium substrate

Hydroxyapatite (HA) powders were prepared by a modified chemical co-precipitation method and electrophoretically deposited onto a titanium tubular substrate. The zeta potential, electromobility and the particle size of the HA suspension was characterized at various pH values and the most stable and dispersed suspension condition was identified. Electrophoretic deposition of the HA particles on the titanium substrate was then carried out at this optimum suspension condition. Studies on deposition rate and examination on the microstructure of the sintered deposit were performed. The stoichiometry of the HA before and after sintering were also confirmed. The deposition experimental data obtained in the present work was also compared with theoretical model proposed in the literature. Lastly, the adhesion strength of the coating was also quantified using shear strength tests.     

Interfacial titanium oxide between hydroxyapatite and TiAlFe substrate

The interface between nano-crystalline hydroxyapatite (HA) thin films and a titanium alloy (Ti5Al2.5Fe) has been studied by means of Fourier transform infrared spectrophotometry and X-ray diffraction at grazing incidence. The HA thin films were deposited by radio-frequency magnetron sputtering in low pressure dry argon on substrates kept at low temperature or heated at 550 °C. The effect of film treatment by sputtering and annealing in humid air, as a simple, effective way of restoring the crystallinity and stoichiometry of the HA bulk, was studied in correlation with the development of a titanium oxide layer at the film-substrate interface. An interfacial TiO₂ film grew at the interface during annealing in moist air, while a TiO₂ layer diffused into the HA films when directly sputtered at 550 °C. The formation of an interfacial titanium oxide layer was inhibited by the insertion of a crystalline TiN buffer interlayer between the substrate and the HA film. Separately, the mechanical characteristics of the different HA films were monitored by nanoindentation to find out how they had been affected.     

ZrO2/hydroxyapatite coating on titanium by electrolytic deposition

In this study, hydroxyapatite (HA) was coated on a titanium (Ti) substrate over a ZrO(2) layer by the electrolytic deposition method, this double layer coating was then compared with a single layer coating of HA. The HA layer was used to increase the bioactivity and osteoconductivity of the Ti substrate, and the ZrO(2) layer was intended to improve the bonding strength between the HA layer and Ti substrate, and to prevent the corrosion of the Ti substrate. The electrolytic deposition formed an HA layer with a thicknesses of approximately 20 mum, which adhered tightly to the Ti substrate. The bonding strength of the HA/ZrO(2) double layer coating on Ti was markedly improved when compared to that of the HA single coating on Ti. The improvement in bonding strength with the use of a ZrO(2) base layer was attributed to the resulting increase in chemical affinity of the ZrO(2) to the HA layer and to the Ti substrate. The osteoblast-like cells cultured on the HA/ZrO(2) coating surface, proliferated in a similar manner to those on the HA single coating and on the pure Ti surfaces. At the same time, the corrosion resistance of Ti was improved by the presence of the ZrO(2) coating, as shown by a potentiodynamic polarization test.     

Preparation of hydroxyapatite coating on CoCrMo implant using an effective electrochemically-assisted deposition pretreatment

A hydroxyapatite (HA) coating is efficiently generated on CoCrMo implant alloys by employing an electrochemically-assisted deposition (ECAD) pretreatment followed by chemical immersion in a supersaturated calcification solution. CoCrMo was electrochemically treated in a calcium- and phosphate-containing solution for short time. A thin layer about 200 nm thicknesses, consisting mainly of amorphous calcium phosphate, was formed on the surface of the CoCrMo after the ECAD pretreatment. After the chemical immersion for 2 h, a layer of octacalcium phosphate was formed on the surfaces. A layer of HA was formed after 72 h immersion. The effectiveness of these treatments was demonstrated by comparison with the alkaline treated CoCrMo. Results showed that the ECAD pretreatment highly enhanced the capability of formation of HA on the CoCrMo surface, while only a small amount of CaP islands were formed on CoCrMo through traditional chemical treatment. A tensile test showed that the coating tightly bonded to the substrate. This work has explored an effective ECAD pretreatment to activate CoCrMo implant surface for generating HA coating.     

Pulsed laser deposition of hydroxyapatite on titanium substrate with titania interlayer

Pulsed laser deposition (PLD) has been used to deposit hydroxyapatite (HA) ceramic over titanium substrate with an interlayer of titania. PLD has been identified as a potential candidate for bioceramic coatings over metallic substrates to be used as orthopedic and dental implants because of better process control and preservation of phase identity of the coating component. However, direct deposition of hydroxyapatite on titanium at elevated temperature results in the formation of natural oxide layer along with some perovskites like calcium titanate at the interface. This leads to easy debonding of ceramic layer from the metal and thereby affecting the adhesion strength. In the present study, adherent and stable HA coating over Ti6Al4V was achieved with the help of an interlayer of titania. The interlayer was made to a submicron level and HA was deposited consecutively to a thickness of around one micron by exposing to laser ablation at a substrate temperature of 400°C. The deposited phase was identified to be phase pure HA by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma spectrometry. The mechanical behavior of coating evaluated by scratch test indicates that the adhesion strength of HA coating was improved with the presence of titania interlayer.     

Sol–gel derived hydroxyapatite/titania biocoatings on titanium substrate

A simple sol–gel method was successfully developed for a hydroxyapatite (HA)/TiO₂ double layer deposition on a pure titanium substrate. Phase formation, surface morphology, and interfacial microstructure were investigated by differential scanning calorimetry analysis (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The TiO₂ layer was coated by a spin coating method at a speed of 1500 rpm for 15 s, followed by a heat treatment at 560 °C for 20 min. The HA film was subsequently spin coated on the outer surface at the same speed and then heat-treated at difference temperatures. Results indicated that the HA phase began to crystallize after a heat treatment at 580 °C; and the crystallinity increased obviously at a temperature of 780 °C. The HA film showed a porous structure and a thickness of 5–7 μm after the heat treatment at 780 °C. SEM observations revealed no delamination and crack at the interfaces of HA/TiO₂ and TiO₂/Ti. The HA film with a porous structure is expected to be more susceptible to the natural remodeling processes when it is implanted in a living body.